The present invention relates to an RF coil and a magnetic resonance imaging apparatus in which magnetic resonance signals are received by a plurality of coils.
Recent magnetic resonance imaging apparatuses employ an RF (radio frequency) coil to generate an electromagnetic field for producing nuclear magnetic resonance in a subject, and receive signals of the magnetic resonance. There have been proposed methods involving providing a plurality of RF coils, Fourier-transforming magnetic resonance signals from the plurality of RF coils, and combining a resulting plurality of images into a new image.
These methods include a method involving obtaining the square sum of a plurality of images employing a phased array, and a sensitivity encoding method involving acquiring a plurality of wraparound images, and arithmetically separating and combining the wraparound image portions. The square sum method combines a plurality of images obtained by a plurality of RF coils using the square sum. In such image combination, one image having a large imaged region is acquired. The sensitivity encoding method performs imaging by an RF coil on an imaged region smaller than a sensitivity region, and separates and combines a wraparound image generated in an acquired image using a sensitivity profile. In such image combination, the imaging time is reduced, or sped up, because the number of phase encodings is reduced.
In these image combining methods, an operator selects the best possible method considering, for example, the required imaged region, S/N (signal-to-noise) ratio or imaging time, and actual imaging is then conducted.
In such conventional methods, however, the operator has to replace an RF coil every time an image combining method is selected and switched. Specifically, the geometry of or spacing between loop coils incorporated in the RF coil is different in each image combining method, and therefore, the same RF coil cannot be used and the RF coil must be replaced.
Especially, for some imaged sites in a subject, acquisition of image information of precisely the same site is required before and after switching the image combining method. The imaging of the same site is difficult because of body motion due to repositioning of the RF coil, for example. Moreover, the repositioning of the RF coil is troublesome for both the subject and the operator, and also it is a factor of lengthening of the examination time.
By these reasons, how to implement an RF coil and a magnetic resonance imaging apparatus in which the geometry of and spacing between loop coils incorporated in the RF coil can be changed without moving the RF coil, is extremely important.